Conventionally, as a soundproofing (sound insulation) or acoustic measure of an architectural structure (e.g., a house, an office building, a plant, and a concert hall), a sound absorption member (or an acoustic member), which is typified by a glass wool or a rock wool, is attached to a ceiling or wall thereof. Among others, from the respects such as economical efficiency, easiness of construction, and environmental safety, a panel member comprising a glass wool is widely used as such a sound absorption member.
However, the conventional panel has a low absorption coefficient, and the sound absorption power thereof is often insufficient for a room having a necessity of room acoustics. Thus, according to the usage, further attachment of a sound absorption panel comprising a porous material or others to a sound insulation panel with a fastening material (such as an adhesive, a nail, or a screw) is also conducted. However, a sound absorption member comprising a porous material (such as a glass wool or a rock wool) usually has a low strength and is easily damaged in conveyance, installation, construction, or the like. In addition, the sound absorption member has a poor sound absorption characteristic, particularly a poor sound absorption characteristic at a low-frequency zone.
Japanese Patent Application Laid-Open No. 2001-081878 (JP-2001-081878A (Patent Document 1)) discloses a sound absorption panel comprising a board-like structure formed by a plurality of cells, a board-like back surface member adhered to the back side of the structure, a long member adhered to both the cut surface of the structure and the back surface member, and a board-like front surface member having air-permeability and adhered to both the front side of the structure and the long member. In this document, examples of the front surface member includes a porous material such as a nonwoven fabric, and examples of the back surface member includes a material having no air-permeability, such as a medium or hard fiber board, a plywood, or a gypsum board. Further, this document discloses that the sound absorption panel has a structural strength necessary for an interior material of an architectural structure, exhibits a sound absorption effect in a wide range of a sound area, is lightweight, matches the interior of the architectural structure, and reduces the cost by simple construction.
Moreover, Japanese Patent Application Laid-Open No. 2002-227323 (JP-2002-227323A, Patent Document 2) discloses a sound absorption panel comprising a honeycomb core member having an opened front face and an opened back face, front face side and back face side permeable sheets overlaid on the front and back faces of the honeycomb core member, respectively, and a back face cover arranged over the back face side of the back face side permeable sheet for forming an air layer between the back face side permeable sheet and itself, and an installation structure for the panel. In this document, examples of the front face side and back face side permeable sheets includes a nonwoven fabric and a cloth. Further, the document discloses that the sound absorption panel and the installation structure for the panel can provide great reduction in weight while securing sound absorption performance equivalent to that of a conventional one or more.
These sound absorption panels, however, have a low toughness or a low rigidity (or stiffness) and have limited uses. In addition, these sound absorption panels have an insufficient sound absorption performance.
Further, International Publication No. WO 2007/116676 (Patent Document 3) discloses that a nonwoven fiber assembly containing a thermal adhesive fiber under moisture is heat-treated with a high-temperature water vapor to produce a hard shaped product having a nonwoven structure (or nonwoven fabric structure) and having the thermal adhesive fiber melt-bonded at a uniform bonded ratio in a thickness direction. This document discloses that the hard shaped product is available for a building board.
When the hard shaped product is used for a building board, however, a high soundproofing or sound insulation property necessary for room acoustics or others is unsatisfied. Moreover, although the hard shaped product has a form or configuration stability which allows use of the shaped product as an independent board, the sound insulation property of the hard shaped product is insufficient due to the fiber aggregate structure. Further, this document is silent on a structure of a panel, and the like.
Moreover, conventionally, for the purpose of sound insulation, a panel (a sound insulation panel) used for a component member (e.g., a door, a wall, a partition, a ceiling, and a floor) of an architectural structure achieves an effect of intercepting sound or noise by increasing a sound reduction index (or sound transmission loss) thereof. It is widely known that a sound reduction index depends on the mass law. However, for a sound insulation panel of a building made by a lightweight structure (such as a wooden or steel structure), the weight increase of the panel is restricted by structural or economic circumstances. In particular, for a movable partition or a fitting (or fixture), a lightweight one is required in order to improve the operationality.
Since it is difficult to improve a sound insulation effect by a panel having a single-wall (single-board) structure, a sound insulation panel having a double-wall structure is widely known as a lightweight sound insulation panel having a large sound reduction index. For the double-wall structure, a wooden or metal rail member (frame member or bar member) is used to fix (or join) a front surface member and a back surface member with separation (or at an interval). However, the rail member transmits the solid-borne sound and reduces the sound reduction index of the sound insulation panel. Further, it is known that a distance of about 200 mm between both surface members of a double-wall structure is effective. However, since a sound insulation panel having a large thickness reduces an interior space of a room, there is a limit to thicken the sound insulation panel. Thus, in order to reduce the thickness of the panel and secure a necessary sound reduction index, a sound absorption material (e.g., a glass wool) is disposed between both surface members forming the sound insulation panel. In other words, for the formation of a lightweight sound insulation panel, the rail member, which fixes (or joins) both surface members with separation (or at an interval), is required, and installation of the sound absorption material between both surface members is effective.
As a type of lightweight sound insulation panels, Japanese Patent Application Laid-Open No. 10-61342 (JP-10-61342A, Patent Document 4) discloses a soundproof door in which a door main body has a double-wall structure formed by an outer frame and surface boards added and provided on both faces of the outer frame, and a reinforcing rail member comprising an elastic body and fixed between both inner and outer surface boards is disposed inside the door main body. In the soundproof door, a sound absorption member (e.g., a glass wool) is filled in a clearance of the double-wall structure, and solid-borne sound is reduced by forming the rail member with the elastic body (e.g., a styrene foam).
However, since such an elastic body has a low strength, it is difficult to secure a sufficient strength against a force which pushes the surface member. Thus a wood or metal material having a strength has to be used for the frame of the panel. Moreover, in order to improve the sound insulation property, an additional sound absorption member is necessary along with the double-wall structure. Further, since such a fibrous sound absorption member (such as a glass wool) hardly has a compressive strength and has no freestanding property (form or configuration stability), a rail member is necessary. However, a sound wave which transmits a panel provided with the rail member and the fibrous sound absorption member induces a transmission resonance, and the sound insulation property is decreased.
Further, Japanese Patent Application Laid-Open No. 2000-250562 (JP-2000-250562A, Patent Document 5 ) discloses a soundproof panel in which a frame is formed by vertical rails, horizontal rails and a middle bone to a framework of a square shape, thin front surface boards are affixed to both inner and outer surfaces of the frame, and middle rails consisting of a plurality of sheets of rectangular strip-shaped reinforcing boards are respectively attached to rear surfaces of both inner and outer surface boards and arranged in a liberated and alternately non-confronting state without contact between the vertical rails and between the horizontal rails facing each other of the frame. In this panel, the middle rails for fixing both inner and outer surface boards of the double-wall structure are separately arranged between the inner and outer surface boards, the inner and outer surface boards are disposed in a non-contact state by interposing a buffer therebetween, and a fire-retardant and soundproof material (e.g., a glass wool) is disposed in spaces existing both left and right sides of the middle rails.
The panel, however, has a complicated constitution of the rail member. Moreover, a wood or metal material having a strength has to be used for the frame of the panel. In addition, in order to improve the sound insulation property, a sound absorption member is necessary.
Meanwhile, the sound insulation panel requires translucency or transparency depending on applications. For example, Japanese Patent Application Laid-Open No. 2006-299789 (JP-2006-299789A, Patent Document 6) discloses a translucent soundproof board in which a translucent sound absorption member and a transparent sound insulation member are attached on a panel frame with some distance kept therebetween, wherein the translucent sound absorption member is formed by piling up a translucent film material and a translucent porous board. In this document, examples of the film material include a synthetic resin film, and examples of the porous board include a net (or mesh) porous body formed by a synthetic resin, a glass, or a metal material. In this translucent soundproof board, however, the sound insulation property is hardly compatible with the lightness in weight.